Lect 2 - Digital Circuits Static Circuits Classical CMOS...

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Static Circuits Digital Circuits Dynamic Circuits CVSL Transmission Gate CMOS Classical CMOS TSPC Logic NORA Logic Domino Logic Classification of CMOS Digital Circuits
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V G Metal Oxide Oxide layer 10-50nm P-type doped Silicon V B MOS Structure forms a Capacitor
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P-type substrate acts as one of the electrodes of MOS Capacitor E 0 φ F = ( E F E i )/q = kT/q ( ln(n i /N A ) q φ Fn = kT/q ( ln(N D /n i ) q φ Fp - Ve +Ve Fermi Potential Work Function q φ S =q χ + ( E C -E F ) Energy required for electron to Move from fermi level to free space. q χ E C 1.1eV E i q φ Fp E Fp E V Energy Band Diagram
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Metal Semiconductor Oxide E 0 E Fm E C E V q χ = 0.95eV q χ = 4.15eV q φ M 4.1eV E C E i 8eV E FP E V Æ When the three components are brought into contact
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Work function of the doped silicon = q φ S = 4.15eV + 0.55 eV + 0.2eV = 4.9eV Work function of Aluminum gate = q φ M = 4.1eV Built in potential difference across MOS system is q φ M -q φ S = -0.8eV
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Work function difference ---- Energy band at surface bends Voltage drop across MOS - Work Function Difference q φ M -q φ S E C E i E Fp E V Al Oxide Semi-conductor Energy band diagram of MOS System Surface fermi level move close to intrinsic fermi level. Fermi potential at surface φ S is smaller in magnitude than bulk Fermi potential φ F
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Flat band Voltage V FB = φ M - φ S
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Lect 2 - Digital Circuits Static Circuits Classical CMOS...

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